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- Geers, Christine, 1982, et al.
(author)
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Properties of Alumina/Chromia Scales in N2-Containing Low Oxygen Activity Environment Investigated by Experiment and Theory
- 2017
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In: Oxidation of Metals. - : Springer Science and Business Media LLC. - 1573-4889 .- 0030-770X. ; 87:3-4, s. 321-332
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Journal article (peer-reviewed)abstract
- The FeCrAl alloy Kanthal APMT™ was exposed to N2–5%H2 at 900 °C. Trace oxygen in the gases supplied an oxygen activity which was sufficient to render alumina and chromia thermodynamically stable. The exposures revealed that the oxide scale was penetrated by nitrogen exclusively at chromia domains. Microscopic analyses of the oxide scale did not reveal micro-cracks that could serve as points-of-entry for nitrogen. Instead it is suggested that nitrogen is transported through a dense chromia layer. Density functional theory was employed to investigate decisive nitrogen surface chemistry and transport properties in chromia and alumina. The study was used to validate that the complex redox chemistry of Cr3+ as opposed to Al3+ is a sufficient discriminating factor between alumina and chromia, facilitating N2 dissociation and mobility of N in chromia.
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| 2. |
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| 3. |
- Mortazavi Seyedeh, Nooshin, 1986, et al.
(author)
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Interplay of water and reactive elements in oxidation of alumina-forming alloys
- 2018
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In: Nature Materials. - : Springer Science and Business Media LLC. - 1476-4660 .- 1476-1122. ; 17:7, s. 610-617
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Journal article (peer-reviewed)abstract
- High-temperature alloys are crucial to many important technologies that underpin our civilization. All these materials rely on forming an external oxide layer (scale) for corrosion protection. Despite decades of research on oxide scale growth, many open questions remain, including the crucial role of the so-called reactive elements and water. Here, we reveal the hitherto unknown interplay between reactive elements and water during alumina scale growth, causing a metastable ‘messy’ nano-structured alumina layer to form. We propose that reactive-element-decorated, hydroxylated interfaces between alumina nanograins enable water to access an inner cathode in the bottom of the scale, at odds with the established scale growth scenario. As evidence, hydride-nanodomains and reactive element/hydrogen (deuterium) co-variation are observed in the alumina scale. The defectrich alumina subsequently recrystallizes to form a protective scale. First-principles modelling is also performed to validate the RE effect. Our findings open up promising avenues in oxidation research and suggest ways to improve alloy properties.
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